[Spatio-temporal distribution of TN and TP in water and evaluation of eutrophic state of Lake Nansi].

Based on the seasonally investigating data from Lake Nansi during 2010 to 2011, the spatial and temporal distribution characteristics of total nitrogen (TN) and total phosphorus (TP) in water were analyzed, and the trophic state was also assessed. The results showed that the average concentrations of TN and TP were 2.617 mg x L(-1) and 0.110 mg x L(-1) respectively. The spatial variations of TN and TP in water were significantly different in four lake regions with the highest value of two parameters (3.830 mg x L(-1) and 0.192 mg x L(-1) respectively) were all found in Lake Nanyang while the lowest value in Lake Dushan (2.106 mg x L(-1)) and Lake Weishan (0.067 mg x L(-1)) respectively. Seasonally, the concentrations of TN in Lake Nansi had no significant difference, but the concentrations of TN in summer (2.805 mg x L(-1)) and spring (3.049 mg x L(-1)) were obviously higher than that in autumn (2.160 mg x L(-1)) and winter (2.452 mg x L(-1)), and that in four lake regions showed no uniform variation trends. While the seasonal change of the concentrations of TP in water were significantly different not only in Lake Nansi but also in its four lake regions, the variation trends were uniform with summer > spring > autumn > winter. Generally, the water quality of Lake Nansi has reached light eutrophication, among which, Lake Nanyang was in middle eutrophic state, while other three lake regions were in light eutrophic state. Integrated analysis indicted that external pollution was still the main influence factors of water quality in Lake Nansi, meanwhile, the pollution caused by pen fish culture was urgent for the control of non-point pollution sources.